Interference reducing method of secret communication



Nov. 28, 1950 M. H. sHAMos ETAL 2,531,951

INTERFERENCE REDUCING METHOD oF SECRET comauNIcATIoN 2 Sheets-Sheet 1 Filed Aug. 2, 1944 INVENTORS JV orrfg H. Siva/210s BY [r1/:nf .5'. oww? r Qui QQ NOV- 28, 1950 M H sHAMos Erm. 2,531,951

INTERFER'ENCE REDUCING METHOD oF SECRET COMMUNICATION Filed Aug. 2, 1944 2 Sheets-Sheet 2 BYl fr v 231g .5'. o we@ ITOHIVFY Patented Nov. 28, V1950 OFFICE INTERFERENCE REDUCING METHOD OF Y, SECRET COMMUNICATION Morris H. Shamos and Irving S. Lowen, New York, N. Y., assignors of one-half to W. I. Westervelt and G. C. Westervelt, both of New York, N. Y.

Application August 2, 1944, Serial No. 547,732

' 5 Claims. 1

We have invented a novel transmission system; and particularly a system for the transmission of intelligence by the radiation of energy in the form of either visible or invisible waves or oscillations. A

In general, the main object of the invention is to provide an eicient, accurate and stable transmission system, the output of which cannot be alected by disturbances or changes in the state of the medium to be traversed between the place from which the intelligence is sent and the place where it is received; cannot be intercepted; and cannot be obstructed or prevented V`from reaching the receiver by jamming Another object of the invention is to provide a transmission system with which intelligence can be sent by either visible or invisible light rays or radio oscillations of moderate or very high frequency, and with complete control of the direction and conditions of transmission.

A further object of the invention is tp provide a system of transmission which can be used to full4 advantage when the transmitter apparatus or the receiver or both are in motion, without distortion or suppression by noise appearing at the receiver; as, for example, when either the transmitter or the receiver or both are carried by a moving object, such as a ship, a plane, or avehicle moving along the earths surface.

These and other objects and advantages of our invention will appear in the following description and all the characteristic features are pointed out in the appended claims. This disclosure, however, is illustrative only, and while the accompanying drawings show one or more embodiments of apparatus which are used, many changes may of course be made in the devices employed, the arrangement thereof, and the method of operation; without departure from the nature of the invention or the underlying principles of same.

On the drawings:

Figure 1 is an outline of one arrangement showing the devices and electric circuits containing said devices, for realizing our invention.

rFigure 2 shows a modified embodiment of our invention; and

Figure3 shows the general character of the Wave energy utilized therewith.

On the drawings, the same numerals identify the same parts throughout..

In the use of the system exemplified in Figure 1, the energy for transmitting signals is obtained from light rays; but in fact any wave length between .000001 cm. and 0.1 cm. may be employed. The numeral l denotesa lamp of sufficiently high power, and light emitted therefrom is brought to a focus and then divided into a pair of beams 2 `and 3. `These beams are polarized; the beam 2 in a substantially vertical plane, for example, as indicated by dots 4; and the other in a substantially horizontal plane, as illustrated by the arrows 5. On one beam the signals are impressed by modulation; and the two beams are then combined again by a suitable lens or other optical arrangement 6, and are sent o" in the form of a single composite beam 1. One component of this beam consists of light poralized in a substantially horizontal plane as before, as shown by the arrows 5, while the other, too, is still polarized in a vertical plane, as now manifested by thedots 5'. This is because modulation is effected by varying or rotating the plane of polarization of the beam 2 and then passing it through a polartelligence as sent from the source.

, of the substance known as Polaroid) which gives passage to only the lightpolarized in a vertical plane. The signals are thus cut off by the lter element 9h, but emerge from the element 9m; because they consist of vertically polarized light and this light is of varying intensity because of the changes in amplitude. The light passing through the element 9h of course does not vary in amplitude of oscillation but is of Vconstant intensity, the same as in the beam 3.

The two divided beams now are separately focussed by lenses Il upon light-sensitive cells l2 and IZm; connected in suitable electric circuits which include a vacuum tube `amplier I3, the anode of which is joined by a conductor I4 to a 3 loud speaker (not shown) or some other reproducing mechanism. The electric circuits are so arranged that light waves of any amplitude reaching the cells I2 and I2m will give rise to opposed electrical impulses; and when the light beams are of equal intensity, though polarized in diierent'planes, vsuch impulseswill cancel themselves or balance outf But when the intensity of the light reaching the cell I2m varies, the

resultant electrical impulses will reproduce the.

intelligence at the loud speaker orotherrapparatus connected to the amplifying meansy I3( We shall now set forth Ymore particularly the apparatus for transmitting. `Adjacent theL-flamp I is a lens I5 which is at the right focal distance from the lamp and directs the light in a single beam against a pair of prisms it' and Il. These prisms are of quartz with top and bottom inthe form of a triangle and they are assembled Lwith the triangles in reverse position; and their longest sidesiinfcontact.#This makesa single unit, oblong iris'hape. '..Thef` quartz: is i'lrst'workedfso that the optic axis of the 'prismi TIt isve'rticaland that of the 4.prism IIY is horizontal. This vfact'isv indicated bythe.f'dots'aandillinesfia and 5a respectively. Thusthe 'two'elements I and vI 'l' are combined to produce .the well-known Wollaston prism; which both divides `theibeam and' polarizes' `the two branches fthereof. All #of the polarization I is brought aboutinthepart Il, but it is confined to twolplanes, one parallel and the; other normal tolthe optica'xis. 'There'. is noi refraction in the part' If-buti whenzthe light thus polarized enters therpart' I6; `the'beam is splitv and the polarized beams.' are separated. The divided' 'beams have unequal velocities 'andu hence must travel .in diiferent -zdirections. .One' beam issues i as the vertically polarized' beamf 2 Land the other' as the horizontally. polarized v'beam' 3 already described.

Ihe Imodul'ator I 8f which impresses the signals 'onwthebeam-.izrnay be either aKerr cell oran electromechanical device. Theiintelligence, the mediumior which may be spoken' words, orV anythi'ng-'else perceptible by thehuman'senses, is 'addressed-'to "afmouthpiece 'or `microphone which," through the usuallinstrumentalities'in a aesnes light of the beam 2 is still vertically polarized but is of varying amplitude according to the modulation.

The horizontally polarized oscillations of the beam 3 are of the same amplitude as at the source i andunless otherwise stated, thisamplitude may be regarded as constant, as already described.

At the place of reception, after the two sep- Ilarated beams impinge upon the elements I2 and l through apairof'local circuits comprising a conductor 22,' a common battery 23 and a pair of E2m, the electrical impulses thus created surge #electric resistancesaZI. The conductor 22 unites case 20,* converts sound waves into electricalv impulses v.upon "metallic :conductors These impulses or oscillations are carried by way of a connection ZI to .the modulator'. I8. Assuming the same'to :be afKerr cell, consisting of a container with'."nit-robehzenel and.` a pairY ofelectrodes immersedtherein vand1connected' tolbe influenced bythe incoming' electrical oscillationsf/ this1 cell operates in Vits 'well-known way Ato rotate the planeetpolarizationof the light passing through `thecell. The electrodes appear in top edge View in lligureZl,` and'have lthe'iorm` of the usual at platesparallel to v'the direction of the -light beam, which passes between them. Hence, as onel speaks into themouthpiece at I9, there are changes ef potential between theelectrodesin the cell vand rotation'of the plane `of *polarization 'in Ygreater orrlesserdegree follows. Of course, fthev planes of #polarization can lbe other *than 'vertical' or horizontal, so longv as they are VVseparate .and distinct.

tThe element 9 betweenl the modulator l'and thelens'or lens arrangement' E allows vertically polarizedA light toa pass without diminutionof intensity. r" No horizontally'plarized light can go through, howeveryand light that is'polarized vin a'- plane 'rotated va'.way"froir1 `thervertical by the modulator I8 can get through "with-amplitude lessened. Hence,4 beyondl. the element.VV 9,.a'll1athe the light-sensitive cells I2m and I2 and the positive pole Of'the'battery 23 is connected to this conductor. One' of the resistances is connected L"to Ythe 'cell I2 `anda-the other to the cell I2m, and

their opposite terminals are joined together. These resistances are adjustable, and the common terminal thereof is connected to the negative pole of thebattery 42 3.

"It will 'thus be apparent that if light waves of the same ampl-itudefall upon the two cells. I2 and I2m, the cells having like characteristics, the resistances 2li being equal, then the impulses in the circuit of Veach 'cell Vwill be equal andbalance out. -i If -one beam istmod'ulated,` the resultant electrical impulses; in these local circuits Will correspond to the variations 'in the energy of the incoming oscillationsfb'earingthe intelligence.

The `outputterminalofthefcellz IZm lis connected by a'conductorf 2'5Jtothe1 control grid of ther tetrode f amplifier I3, ".theanode lfandf cathode circuits of which are offthe-Lusual'type. The resultant oscillations are 1 thus :amplifiedlaxid 'conducted to the leady Ill ftolfbelreproducted by`lthe loud speaker or other reprducingpparatus. To the' common rterminal Vofthe r'esistances?, allead v251s fjoined'by a sliding! contact jl'this -l'ead being also connectedtoa tube-'amplierl 2li of the triode type. The :circuits 'offthe electrodes of this tube 2l are V'connected;ini-fthe liivell"`-kno`wn way; v`and in 'the'cathodff-'thistbaandif--the ampl'ier -I3 Ais al condenser--off-large capacity '28 rto by-pass the signal va'riatins'A and lthuss'upply steady' bias'. lThe cathodes -of-.the'` tw tubes may be of the larneht'or the iheaterftypefpreferably the latter. yFromv thecath'ode of-'fthe tube 2"! -a conductor' runs to another4 'grid -in thef amplier 13|; and toavoidesig'nalinterfe ncela'ff'chokeicoil 25!V islplacedv in thelineof 'sai' r'a'ductor. A simi- `lar Echokefc'oil 29a isputfin theflineof the conductor'. A'For the-amplifier: I3f`=the 'usual grid 'leak-"3!! is'provided. Coupling v'condenser'v i3dis inserted inthe lead-25" betweenf`the' gridileak and thev terminal of the ladjacer'ii' resistances 124 to'isolate-the tube i3 flornfthbattery`-23.

nThe function and purposeof the'itube'mZ'I Ais-to maintain the eiect of the'ampliflerfl 3 in case-the to compensate for any variationimtheoverall intensity of thesource. Then the-'potential caused by-the cell I2,'dueto thecontr'ol b'eam'impinging thereon is-amplified bythe-tube 21. =`This amplied V'Voltage is appliedtothe-s'crcerr gridl'of'the amplier I3, raising the potentialf'ijff'tli-isy grid, so that-the effe'ct-Of the tube l3 Yrrilfal'ls constant. Thus, tube 2l and its associated" circuits fc'omprise, YYin 'eiect,- ai meansv of `autmatic"=volume control.

-A' system of l the kind above described-*willi not be' disturbed by" variationsf in? the' state. of fthe f inter'vening'medium; suchasl staticglfog-Tsmoke'or other cause of fluctuation intheiamouhtofl light received-and'.ordinarilyappearing as'fnoiseimtme receiver. Any such variations will aiect the tw polarized components equally, creating equal and opposed electrical impulses which eliminate one another beyond the cells |2and |2111.. vOnly the signal impulses produce oscillations in the receiving circuits which reach the devices beyond the amplifier i3.

Previous methods of static elimination in radio transmission consisted primarily in the transmission of two beams, one carrying the intelligence, the other being the control beam. However, these Ytwo beams were of different carrier frequencies, so as not to interfere with one another. Hence, the band width is widened and, since noise is proportional to band width, the amount of interference to be eliminated may become so great as to overshadow and suppress the intelligencehence, no such balancing system can be effective. In our system, the frequency of the two polarized phases is the same, and the band width is limited by the modulation frequency; and the elimination is complete.

A system of this kind affords full security and secrecy because of the possibility of arbitrarily modulating the light at the source as indicated i at S on Figure 1. This modulation could be of any chosen type or pattern. It would alect both divided, polarized beams 2 and 3, be delivered to the light-sensitive cells l2 and |2m equally and be balanced out through the resistances 24; the

same as any outside disturbances inuencing both polarized components of the beam 7. But the signals impressed on one beam by the modulator I8 will go through without distortion, to create impulses in the receiver by which the intelligence is converted into perceptible form.

In consequence, an enemy observer attempting to intercept the beam with ordinary photophone apparatus will get a signal so masked by noise that the information will be unintelligible. Furthermore, this system has the important advantage that no knowledge of the nature of the scrambling procedure at the source is required by the operator at the receiver. Thus, the scrambling need not be systematic, but may be entirely random. The usual security systems employed in radio and adapted to photophone transmission, have twoV defects; first, the operator at the receiver, as well as the operator at the transmitter, must be informed of the scrambling procedure; and second, the scrambling, being systematic for at least short intervals of time, is thereby capable of being deciphered. In addition, our invention makes it unnecessary to employ complex filter circuits.

Our system affords the additional advantage over ordinary photophone systems, of being useful in places where either the transmitter and/or the receiver are in motion; such as between ship and shore, ship and ship, ship and plane, plane and plane, plane and ground, or vehicle upon the ground. In ordinary systems without control beams, relative motion between the transmitter and receiver causes variations in received intensity which result in noise capable of masking the intelligence; but in our system such noise is eliminated, provided of course the rotation of the beams is not such as to bring about complete cut-off.

Figure 2 illustrates apparatus by which radio oscillations of moderate or high frequencies can be utilized to give the same results as above set forth. The transmitter is outlined at T and comprises two antennae members 3| and 32. The carrier wave is polarized in one plane and propa- 6 gated from member 3| (inc 'ned at 456) of an antenna; and another wave of the same frequency is polarized in a plane at right angles to the rst and sent out from the member 32 of said antenna, also inclined at 45 in the opposite direction, and at right .angles to the member 3|. The two polarized 4components of the beam are thus forwarded together. At the receiver they are picked up by similarly inclined antenna members 33 and 34, at right angles to each other, and delivered to suitable mixing circuits where all the oscillations are balanced out except the signal impulses, which reproduce the signals and render them intelligible.

The antenna members 33 and 34 are separately grounded through conductors 35 and 36. In the line of each conductor is the primary winding of a transformer 33, commonly known as the antenna coil. The secondaries of these transformers have` a common terminal; and across each secondary, commonly known as the radio frequency coil, is connected a` tuning condenser 38. The opposite terminals of the secondaries of the transformer are attached by wires to the control grids of a pair of pentode amplifiers 4.0, with both screen and suppressor grids. The common terminal of the secondaries is joined by a wire 39, having a suitable ground tap, to the negative pole of a common plate battery 43 for the amplifiers 433. The positive pole of this battery is joined to the midpoint of a transformer primary coil 4, the opposite terminals of which lead as shown to the anodes or plates of the amplifiers 43. The transformer secondary coil 45 leads to the reproducer of the intelligence. The cathodes of the tube 4U are preferably of the heater type, with by-pass condensers 4| and bias resistors 42 in circuit therewith, and joined to the conductor 39. The connections of the tubes 43, transformers, etc. need not be described in further detail, as they are arranged in the well-known way so that oscillations of equal frequency, amplitude and phase picked up by the antenna members 33 and 34 create impulses which are balanced out in the anode circuits of the tubes; while the intelligence modulations create unbalanced impulses which take effect in the reproducer circuit. The tuning condensers 38 are coupled mechancially, as indicated by member 38a, so as to provide tuning of both circuits simultaneously.

The antennas 3| and 32 polarize the waves in the respective planes of inclination, and they are inclined at 45 so that each will transmit its full equal share of disturbances creating noise at the receiver. Static is picked up at the transmitting antenna and imposed on the modulated carrier wave emitted therefrom. In the space between the transmitter, the waves are not inuenced by any disturbances from which noise at the receiver might ensue. At the antennas 33 and 34 the incoming oscillations will include whatever comes from the transmitter, with disturbances at the site of the receiver added. All of these are divided between the antenna members 33 and 34 and opposed and eliminated in the tube circuits. But the modulations of the carrier wave are passed through to the secondary coil 45.

Figure 3 shows diagrammatically the combined carrier and intelligence oscillations in planes apart. `The control vwaves of constant amplitude, unless disturbed, are indicated at 3|a, the modulated intelligence waves at 32a, They are propagated in all directions unless the frequency, is very high or the antenna members are designedas directional:

If the antenna memberhS-Il were-vertical, the

carrier-or control beam. would be-polarized in a Vertical; plane andfsince any disturbances at the receiver might'. likewise be`V polar-ized mostly in the same plane,Y the1di'sturbing oscillations. would not be. equally divided between `the-members 33l and'lhand no. balancing outy would follow. If' necessary, the -modulated beam andthe control beam 4may beof different `amplitude `-so as. to providea component of carrier frequency at the. receiver for efficient detection.

So far. as the transmitteris;concerned, a single polarized wave modulated to carryatheintellh. gence could be employed; and thefseparatercontrol beam omitted.. The intelligence. would fthen. be propagated as in ordinary radiotr-.ansmissionsystems.V But'at. the receiver, this Wave:vvvou-ldil be-.subjectto all the disturbancesthatgivelfrisev totthe. usual site noises; and these. would Vnoti be.. eliminated in the receiver: circuits. The arrangement of .the antennamembers of both the. transmitter and receiver 1 at the. inclinations stated with each pair of antenna memberswatr right'. angles to. each. other; andthe propagation ofthe polarized control wavefrompne-antenna. member of the transmitter, andthe intelligenceI inv .a.separate, polarized bea-m zfrompthe other; followed by. the separate receptionof each ona correspondingly inclined. antenna...member,` ene.a able us tovrealize. allof thebenets and advantages of our invention.

The system` of Figure 2is.: accurate and incapable of :interception or jammingi Thecir.-

cuitstof' vthe. antennamembers. 311 and 32:;are of;-

the conventional kind, andmayinclud'ermeansi for. modulating.. both ,beams in faddition:.to-:im:-l pressingthe intelligence-on.one,.-as1.before.c Such: additional arbitrary modulation willlbalanceout;

as. in the system of. Figure 1i: wherefmodu'lation at the light source AI .as well as byitherrdevice 48;. maybe effected. Secrecy of .transmission will. be assured,because any.- one tuning,ini-.Will'refV ceive only transmission effects that are noisys-and. unintelligible.;

Our. invention. is very useful :in-fthe. rieldfoii` television and. because.. of. its.. freedom from. inf. terference and' disturbance of eVery..sort-,a.it canl bei employedto transmit pictures oven-consider.'- able distancesl with only relay @stationsin:v b'etween, and make.'thecostlyzcoaxiala,cable,;with: its casing lilledzwith gas yand transmitting@ .conductorpthereim entirely unnecessary;l

Having described our. inventiim,.wha1r we claim; to benew is:

1. A method ofk transmitting. intelligence cone; sisting inv creating light energy;.dividingzzsaidl energy intotwo vseparate beams: and:simultanea`v ously'polarizing `eachfin separate planesl,f;mo.dur1 lating one of saidbeamsby rotatingitsi-planes'o polarization, confining said beamfrthereafftervto: its. original plane. offpolarizationnto varyftheamplitude of the oscillations thereofaccordinglto.` the modulatiomcombining saidfbeamsfand-lpropa-J gatingfsame togetheras, a composite beam, separating-thepolarized componentsthereof, and transformingfthe Yoscillations thereof intofelecif trical.V impulses; `opposing the-'impulsesclue.v to said components, and reproducing the intelligence; fromthe resultantfimpulses; f

2.v A-methodoftransmi`tting intelligence whichY consists. in4 creatingat-a. single sourcewave energy CII of higher frequency than visible light rays, dividing' and :modulating a-portion -of vsaid energy, polarizing said portion'in a definite planebetween the place of transmission and a place -of-reception, ypolarizing the remainder of said energy -between said-places,receiving and collecting energy thus-.polarized,A converting the polarized components of said energy into separate electrical= impulses, opposing-the `impulses arising from said portionto vthe impulses due to saidy remainder, and from theresultant impulses reproducing said intelligence.

3.. Amethodaccording to .claim l including. the stepof arbitrarily modulating allsaid energy be.

fore. dividing.. it, in addition to impressing the.

intelligence on one beam thereof, so as. to mask saiclintelligence and prevent unauthorzedrecep-A tion;

4.; A. method according to claim 2 .whichcomf prises thestep of arbitrarily modulating. all saidV to a receiver at saidplace of reception, converting the full energy of the osciliations of both. .saidportion andy said remainder into electrical impulses, opposingtheimpulses due to said.Y portion.

to the oscillations caused by said remainder, and

reproducing said intelligence from the resultant:

impulses, and further modulating alike -inan4 arbitrary manner the portion carrying the intelligence and the remainder of said energy'before emission, in addition to impressing the intelli-- gence upon saidv portion, to prevent ascertain.- ment of saidv intelligence if intercepted.

MORRIS H'. SHAMOS.

IRVING S. LOWEN.

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